An energy recovery apparatus used in the seawater desalination system includes a cylindrical chamber (CH) having a space for containing concentrated seawater and seawater therein and being installed such that a longitudinal direction of the chamber is placed in a vertical direction, a concentrated seawater port (P1) provided at the lower part of the chamber (CH) for supplying and discharging the concentrated seawater, a seawater port (P2) provided at the upper part of the chamber (CH) for supplying and discharging the seawater, a flow resistor (23) provided at a concentrated seawater port side in the chamber, and a flow resistor (23) provided at a seawater port side in the chamber. A circular plate (30) having a hole at the center thereof is provided between the concentrated seawater port (P1) and the flow resistor (23), or between the seawater port (P2) and the flow resistor (23).